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Author Topic: Big fan into little fans increase air flow?  (Read 1885 times)
Big Time Coin
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July 03, 2011, 04:50:03 AM
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I searched and couldn't find anything on this.  I am planning to have big box fans blowing into smaller fans in an attempt to increase airflow.  Does that work?  I don't know much about fluid dynamics physics, but it seems like common sense that it will increase the air speed if you have the air already sped up when it hits the smaller fan.   Huh

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BitPorium
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July 03, 2011, 04:58:41 AM
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can you show a pic of your current setup?  a box fan might not be the greatest option.
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July 03, 2011, 05:23:14 AM
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http://img818.imageshack.us/img818/7249/1002139k.jpg
http://img268.imageshack.us/img268/6072/1002140h.jpg

The insert image function isn't working for me with these hotlinks.  Anyway, there you go.

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July 03, 2011, 05:29:27 AM
 #4

To make a complicated answer easy: If you have sufficient exhaust in the duct (aka case), the addition fans will increase flow. If there isn't enough exhaust, then the pressure will act against the fans and cause less airflow.

There are also concerns of the first fan's cfm being less than the second fan*, causing the first fan in the series to have no effect or burn the motor out, since it'll be spinning from the power of the oncoming air instead of the motor.

Do keep in mind that the physics are very dependent on the setup, so result may vary. I'd suggest experimenting for shortish periods to see if you get temperature changes.

Code:
*Fan setup (arrows indicate flow direction): [<-Case][<-Fan1][<-Fan2]
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July 03, 2011, 06:24:38 AM
 #5

See I'm thinking about wrapping it all up with a tarp and cutting holes to run 4" ventilation ducts to the outside to exhaust.  I would have preferred a larger diameter exhaust pipe, and I'm not sure if the small diameter will be sufficient.  I might want to put a little fan in the exhaust duct itself to increase airflow.  What do you think about that idea?

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July 03, 2011, 10:02:45 AM
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I dont think the box fans are doing much for the lower systems. what i would do is try to lower the ambient temperature. It seems that airflow is fine. i would try to position the system a little closer together and then put that tarp and then lower ambient temperature.my setup is much smaller but I have an air conditioner running, really makes a huge difference. Also remember Hot air rises, so your in effect pushing all the hot air that is rising back into your system. What i would do is move fans from above to the side, PCB side not fan side. To help push some air away. Or do what i do. Have 2x 10000 btu air conditioners running 24/7, Keeps my room at a toasty 60f!

my current setup. I just  have an AC blowing cold air to my ceiling and a ceiling fan moving things around. its not the mose efficient systems because I have to cool down warm air but it works fine for now. PS. its like that untill i get my extender cables. But the same principles apply to you. just try to move cooler air towards the cards, dont try to cool them with your fan. Or you could try ducting each fan and provide it with enough presure to keep them going and the exhaust all the warm air. But that will take a crapload of time.
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